No real help with the Wacom issue. You can try disabling (rename it) the file devicerc which is in the Gimp 2.9 profile. C:\Users\Appdata\Roaming\GIMP\2.9 (I think that is the Windows path)
Dive into the Input Device settings and let Gimp make a new one.

When it comes to versions, the Gimp 2.9.5 was from partha.com Is that correct?
Which 2.9.8/9 version are you upgrading, there are Windows versions from partha, gimp.org also samj.